1. Field of the Invention
The present invention relates to a process for semiconductor devices and more particularly to a process for integrating light energy transmit and/or receive functions with existing semiconductor devices, such as GaAs or InP devices.
2. Description of the Prior Art
Various semiconductors are known, such as high-electron mobility transistor (HEMT) and heterojunction bipolar transistor (HBT) active devices as well as light-emitting devices, such as laser diodes, in which it is necessary to monitor performance of the device during operation. For example, for light-emitting devices, such as lasers, performance is normally monitored by way of a photodetector. The photodetector is used to monitor the intensity of the light indicating device. Such photodetectors are known to be fabricated separately and epoxied directly to the light-emitting device. However, such a process is relatively inefficient since it requires separate processing of the photodetector and also requires attaching of the photodetector to the semiconductor device. Such an inefficient process thus increases the cost of devices which require monitoring.
As such, processes have been developed for integrating photodetectors into a light emitting device, such as a laser, for example, as disclosed in U.S. Pat. Nos. 5,757,837 and 6,023,485. However, the integration of the photodetectors into the light-emitting devices as disclosed in these patents involves relatively complicated processes and only provides limited performance. For example, U.S. Pat. No. 5,757,834 discloses a vertical cavity surface emitting laser with an integrally formed photodetector. The photodetector is formed as an intracavity quantum well photodetector, disposed at the optical intensity peak at the Fabry-Perot wavelength. In particular, the laser is formed on a GaN substrate and includes an n-doped distributed Bragg reflector (DBR) mirror stack. An active gain region is formed on top of the n-doped DBR mirror stack and includes a one wavelength spacer and a quantum well stack. A p-doped DBR mirror stack is formed on top of the active gain region. The intracavity quantum well photodetector is formed on top of the p-doped DBR mirror stack and includes a 5λ/4 spacer with an In0.2 Ga0.8As quantum well. On top of the photodetector another n-doped DBR mirror stack is formed.
The laser emits light from the underside of the GaAn substrate. Reflected light is sensed by the photodetector to provide an indication of the intensity of the laser light. Although the system disclosed in the '837 patent discloses an integrally-formed photodetector, the processing steps are rather complicated and include the formation of a quantum well sandwiched between two DBRs.
U.S. Pat. No. 6,023,485 also discloses a vertical cavity surface emitting laser diode with an integrated PIN photo diode. In this embodiment, the PIN diode is formed on top of a vertical cavity surface emitting laser. The PIN diode is formed as a lower stack of n-doped DBRs, which are shared with the laser. An intrinsic region and p-doped upper stack of DBRs are formed on top of the PIN diode. Ion implantation is used to damage a portion of the upper stack of DBRs in order to define high resistivity damaged areas to confine the light paths in the region of the upper stack of DBRs. As such, the device is relatively complicated to fabricate. Thus, there is a need for a monitoring device that can be integrated with various active devices that is relatively simpler to fabricate than known devices.